feat: add replace subcommand with multi-pattern support

tests/unit/replace_parser_test.go

@@ -0,0 +1,31 @@
+package replace_test
+
+import (
+	"testing"
+
+	"github.com/rogeecn/renamer/internal/replace"
+)
+
+func TestParseArgsHandlesWhitespaceAndDuplicates(t *testing.T) {
+	args := []string{"  draft  ", "Draft", "draft", "final"}
+	result, err := replace.ParseArgs(args)
+	if err != nil {
+		t.Fatalf("ParseArgs returned error: %v", err)
+	}
+
+	if len(result.Patterns) != 2 {
+		t.Fatalf("expected 2 unique patterns, got %d", len(result.Patterns))
+	}
+	if len(result.Duplicates) != 1 {
+		t.Fatalf("expected duplicate reported, got %d", len(result.Duplicates))
+	}
+	if result.Replacement != "final" {
+		t.Fatalf("replacement mismatch: %s", result.Replacement)
+	}
+}
+
+func TestParseArgsRequiresSufficientTokens(t *testing.T) {
+	if _, err := replace.ParseArgs([]string{"onlyone"}); err == nil {
+		t.Fatalf("expected error when replacement missing")
+	}
+}